Arrangement for testing spark plugs



L, @Mmmm En" ARRANGEMENT FOR TESTING SPARK PLUGS Filed Deo. 22, 1933 Pat'ented Oct. 16,.` 19/341 ARRANGEMENTPF on TESTING SPARK was Emile Louis Grangier and Fernand Niogret,

' Lyon, France Application December- 22, 1933, se

rial No. 703,618

In France September 23,l 1933 4 Claims.

This invention relates to an arrangement for testing spark plugs for internal combustion engines or the like Spark plugs are liable to many sorts of failures.

5 The sparking terminals may become short-circuited with each other; they may be insulated from each other by an oily layer; they maybecome abnormally spaced from each other owing to corrosion of the metal. It also happens thatthe sparking terminals are connected by a poorly conductive layer of carbon which, while not properly short-circuiting the spark gap, weakens the spark and perturbs the correct ignition.

The arrangement which is the object of this invention permits an easy test of a spark plug in any case. It consists in connecting an oscillating circuit across the plug tobe tested and in detecting the high-frequency current resulting therein from the spark by means responsive only to such a current.

In the annexed drawing:

Figs. 1 to 4 are diagrams adapted to explain the basis of the invention.

Fig. 5 illustrates an arrangement suitable according to the invention.

In Fig. 1, 1 is a coil adapted to deliver hightension currents of relatively low frequency to a spark gap 2. 'An oscillating circuit is connected across spark gap 2, said circuit comprising a coil 3 in series with two condensers 4. Coil 1 comprises a great number of turns of line wire and has an iron core so that it acts as an arrester or choke coil for high-frequency currents. Coil 3 is lon the contrary void of any iron core and com- 35. prises a small number of turns of wire of large diameter.

In operation the condensers 4 are charged by coil 1 and when the voltage is suiiicient the spark flashes at 2. Condensers 4 are then discharged 40 through the sparkgap, thus generating an oscillating current of very high frequency. y

This high-frequency current may be detected by means of a lamp 5 connected across coil 3. The frequency of the current generated by coil 1 being low, the charging current does not light lamp 5 since the resistance and self-induction of coil 3 are negligible with low-frequency currents. But the discharge current having a very high frequency, the voltage difference between the terminals pf coil 3 is sufficient to light lamp 5.

In the arrangement of Fig. 2 lamp 5 is fed by a separate coil 6 which is inductively coupled with coil 3. The operation is the same as in Fig. 1.

When this secondary coil 6 comprises a number of turns large enough with respect to coil 3,

lamp 5 is operated even if there, is interposed in its circuit a small condenser 7. The unavoidable capacities between coil 6, the metallic surrounding parts and the electrodes or terminals of lamp 5 are often sufficient to form a path for the 00 high-frequency current in the absence of any condenser 7.

These arrangements permit of easily testing spark gap 2. When the latter is short-circuited condensers 4 are n'ot charged and lamp 5 is not 55 lighted. When the spark does not take place owing to insulation between the electrodes or otherwise, condensers 4 are charged and then discharged at the low frequency of coil 1 and no high-frequency current is generated; lamp 5 is not 70 lighted. When the electrodes of spark gap 2 are connected by a resistance which weakens the spark, condensers 4 are not charged at the normal voltage and their discharge is damped so that no high-frequency is generated; lamp 5 is not 75 lighted.

In automobile engines and the like the ignition magneto or coil 8 (Fig. 4) generates 'a current o f relatively low frequency. The spark plug 9 is the spark gap to be tested. 'Ihc oscillating circuit 3 4 is therefore connected in parallel with plug 9. Lamp 5 is preferably a small neon glow-discharge tube or bulb. It may be' connected according to any one' of the diagrams of Figs. 1 to 3.

As it has been explained lamp 5 will be lighted only as long as plug will work'properly. 'I'hus any sort of failure will be easily detected.

It is of course necessary that there exists no other source of high-frequency currents than the spark plug 9, otherwise lamp 5 would be lighted even when the ignition fails. With some igniting devices the spark distributor includes itself a small spark gap and not a sliding brush. This spark gap may generate high-frequency currents which perturb the operation of the plug testing device. 'Ihis may be remedied by inserting an arresting lter or choke-coil between thev spark distributor and the spark plug.

As illustrated, Fig. 5, the magneto or ignition coil 8 comprises the fixed or lmovable high-voltage generating coil 1 and a spark distributor embodying a rotating electrode 10 connected with the high-voltage terminal of coil 1, in cooperation with xed electrodes 11 which are somewhat spaced from the path of electrode 10. Electrodes 11 are respectively connected with the individual spark plugs of the engine. For the sake of simpilicity there is shown but one plug 9 and the corresponding oscillating circuit 3 4 (which in this l10- instance comprises but one condenser) provided with the detecting lamp 5. 12 designates a itera ina coil which will he described later on.,

currents across coil l itseli. Under such circumstances, the charging current of condenser Li. through the spark between electrodes i0 and il may he a high-frequency oscillating ctu'rent canoble ci illuminating lamp 5, even ii spark plug 9 has failed through mutual insulation ci its electrodes by oil, for instance:

This is remedied by means oi coil 12. The

' latter is a coil having an ohmic resistance and ja self-induction sumcient to form choke coil for' high-frequency currents, any capacity between its terminals being carefully avoided. Thus, even if distributor 10-11 generates high-tref cuency currents. the latter do not pass through oscillating circuit 3 4 and do not perturb the loperation of the latter.

Another solution of this difiiculty would consist in arranging lamp 5 in a separate oscillating i, circuit 6--7, Fig. 3, oi low ohmic resistance, and

in adjusting the wavelength of the latter in mc-v cord'ance with the wave length of circuit 3 4. This tuned circuit 6,--7 would then be responsive to the osciliationsloi circuit 3-4 and not to :other high-frequencycurrents.l

Walciaim: l. m combination. a high-voltage ignition our rent generator; a spark plug led by said non crater; a nltering coil inserted between said son erster and said plus, said coil hein@ adapted to form a cliche-coil for hiahwirocuencr/ currents; an oscillating circuit connected across said plus; and means to detect high-trennen@ currents in said circuit, seid means hein@ irrcsponsivc to low-frequency ciments.

Zi. In combination, a high-voltage ignition current generator; a spark plusr ieri by said cenerator; a altering coil inserted between said generator and said plug, said coil being adapted to torni a 'choke-coil 'for high-frequency currents; an oscillating circuit connected across said plug, said circuit embodying atleast one coil and at least one condenser; and an electric lamp.-

oacillating'circmt'connected across said plug; an"

oscillating' circuit inductively coupled with said first-named oscillating circuit, said seconde named oscillating circuit having the same wave length as said first-named oscillating circuit when the discharge takes place through said spark plus; and means to detect high-frequency.

currents in said second-named oscillating circuit.- EMILE LOUIS GRANGIER.

FERNAND NIOGRET. 

